Customarily, desk top calculator printers are comprised of a movable carriage for advancing a print head across the width of a record medium which is fed line-by-line past the print head by a main drive mechanism operated off of the print head drive. As the print head is caused to traverse the record medium, a ribbon cartridge will feed a print ribbon intermediately between the print elements on the print head and the record medium in forming selected characters on the record medium. In many applications, such as, point of sale terminals, it is desirable to record calculations performed by the printer on separate record media, for example, in order to provide the customer with a printed copy of the information recorded on the master record. In such cases, it is often necessary only to provide the customer with totalized information and not the preliminary calculations. However, very often the totalized information may require multi-line recording on the validation or customer copy. Moreover, it is desirable that the customer copy be of limited size such as in ticket form which can be readily inserted and removed from the printer without disturbing the master record. In still other cases, it is advantageous to permit printing on separate rolls comprising the master record which are advanced side-by-side through the printer in addition to the validation or customer copy.
In controlling the advancement of the drive mechanisms, various escapement devices have been employed to incrementally feed or index the record medium past the print head. Representative of such devices is disclosed in U.S. Pat. No. 3,986,594, owned by the assignee of this invention, in which a cam-driven pawl engages a ratchet on the platen to rotate the platen and index the record medium each line or space. A separate detent is utilized to normally lock the platen against movement when not being advanced by the pawl. Other patents of interest which disclose paper drive or line feed mechanisms are U.S. Pat. No. 3,429,414 to Bradbury; Hodne U.S. Pat. No. 3,935,938; and Japanese Utility Model Publication No. 44021/1975. In the smaller printers, however, it is important to be able to minimize the power requirements for indexing the record medium as well as to make the indexing mechanism more compact. These requirements are particularly important where separate index or feed mechanisms are required to perform independent line feed operations. Other considerations in multi-function printers of the type described are establishing guide paths for the record media which will not interfere with one another and avoid time-consuming adjustments or special settings.